This invention relates to a starter with a planet gear speed reducer, and more particularly to a water-proof structure about penetrating bolts inserted into the peripheral portion of an internal gear forming the planet gear speed reducer.
A conventional starter with a planet gear speed reducer (hereinafter referred to merely as "a starter", when applicable) is as shown in FIG. 4. The conventional starter 1, as shown in FIG. 4, essentially comprises: a DC motor 2; an overrunning clutch 4 slidably mounted on the output rotary shaft 3 of the starter; and a planet gear speed reducer 5 for reducing the torque of the armature rotary shaft 2a of the DC motor 2 and transmitting the torque thus reduced through the output rotary shaft 3 to the clutch outer 4a of the overrunning clutch 4. The output rotary shaft 3, the planet gear speed reducer 5, and the overrunning clutch 4 are surrounded by the front frame 7 of the starter with the exception of the lower opening (not shown) which is so formed as to allow a pinion 6 integral with the clutch inner 4b of the overrunning clutch to engage with the engine ring gear when the overrunning clutch 4 is slid forwardly. The front frame 7 is fixedly secured to the periphery of the end face of the DC motor 2 as follows: Penetrating bolts 8a are inserted into the DC motor 2 from behind to penetrate the latter with a small clearance formed between the inner wall of the yoke 2b and each of the bolts 8a, and the threaded end portions 8a of the bolts 8 are engaged with the threaded holes cut in the step 7a which is formed on the inner wall of the front frame 7.
More specifically, the penetrating bolts 8 are extended through the holes 9 formed in the end face of the DC motor 2 which is integral with the yoke 2b, over an internal gear 5a forming the planet gear speed reducer 5, and through cuts 5c formed in a flange 5b which is radially outwardly extended from the front periphery of the internal gear 5a, thus reaching the threaded holes 7b in the step 7a formed on the inner wall of the front frame.
As was described above, the front frame 7 has the opening through which the pinion 6 is partially exposed so as to be engaged with the engine ring gear. Because of the provision of the opening, the conventional starter 1 suffers from the following difficulties: Water may go into the frame 7 through the opening. More specifically, it may flow down the penetrating bolts 8, and run through PG,4 the cuts 5c of the internal gear flange 5b and through the holes 9 formed in the end wall of the DC motor 2, into the latter 2; that is, the DC motor may be damaged by the water flowing thereinto through the opening formed in the frame.